1. Field of the Invention
This invention relates to the field of ignition systems for internal combustion engines, and in particular to an improved lobe sensor arrangement for use in an electronic ignition system for internal combustion engines, the system deriving a signal for initiating the generation of the spark in spark plugs based on the position of the distributor camshaft.
2. Brief Description of the Prior Art
Electronic distributor ignition systems for replacement of point type distributors are well known in the art. Basically, such electronic ignition systems receive their timing information from the distributor camshaft and convert the rotational position of the camshaft into a series of pulses for ultimately creating a spark for distributing to the spark plug in a timed relationship to the rotation of the distributor camshaft. Several electronic ignition systems of the prior art modulate a source of either magnetic or optical flux. A remote sensor monitors the modulated signal. Electronics within the sensor analyzes the modulated signal and transmits a trigger signal for the spark. Synchronization of the modulation source with the position of distributor camshaft insures proper timing of the spark.
The use of Hall-effect devices in electronic ignition systems is also known in the art. In some cases, a single magnet and a single Hall-effect device are spaced apart, and a rotatable object timed with the camshaft passes through the magnetic flux between the magnet and the Hall-effect device, inducing an output from the Hall-effect device. In other arrangements, a pair of magnets with a single Hall-effect device between them, or a pair of Hall-effect devices with a single magnet between them, are employed, but the same technology is relied upon, i.e. producing spark timing pulses by the passing of a rotatable disc-like object, or objects, within the magnetic field, or fields, standing between the magnet(s) and Hall-effect device(s).
One such prior art device can be found in U.S. Pat. No. 5,406,926 to Huan-Lung Gu. This reference shows, in one embodiment, a spark ignition system for an internal combustion engine having a radially extending vane mounted on the distributor rotor shaft and rotates therewith. The vane, at its radially outer end has an axially extending portion which passes by a Hall-effect sensor. The number of axially extending portions is the same as the number of cylinders. The distributor rotor is also mounted on the shaft and is spaced from the vane. An integral part of the apparatus is a stray noise isolating plate (10) extending across the distributor and separating the rotor from the vane. As the shaft rotates, a signal is generated to initiate the spark. Other embodiments have multiple vanes for generating additional signals used for other engine functions. Another embodiment shows a distributorless system with a plurality of coils. There is no distributor rotor, but the top of the unit is closed by the stray noise isolating plate. In some embodiments, the second vane is asymmetrical and provides a signal for fuel injection. While not specifically called out, the structure shown seems to indicate that the axially extending portion passes between the Hall-effect unit and a magnet.
U.S. Pat. No. 5,158,056 to Raymond King shows an ignition system for a spark ignition engine in which a hub is mounted on the camshaft and has a plurality of magnets mounted on the periphery of the hub. A stationary magnetic sensor detects each magnet as it passes during each rotation and generates the signal for the spark ignition.
U.S. Pat. No. 5,127,387 to Haruyuki Matsuo shows a spark ignition signal generator in which a radially extending plate is mounted on a shaft rotated by the engine. At the radially outer end of the plate are tabs bent to be axially oriented. A stationary magnet is positioned in spaced relationship to the Hall-effect unit and the tabs pass between the Hall-effect unit and the magnet on each rotation. The apparatus is directed to the particular shape of the plate.
U.S. Pat. No. 5,126,663 to Izuru Shinjo shows the detailed design for a particular type of mounting for a Hall-effect unit in which a spring type arm provides a resilient force to the plate on which the Hall-effect unit is mounted, and this provides no distortion to the Hall-effect unit.
U.S. Pat. No. 5,097,209 to Alfred J. Santos shows a spark ignition system for an internal combustion engine. A plate is mounted around the shaft of the distributor and extends radially outward. A pair of rings are on the plate, and each has a plurality of magnets in space apart relationship mounted thereon. Hall-effect units are fixed in place and detect the passage of the magnets. Two Hall-effect units are used to detect the outer ring of magnets to provide two signals for each passing magnet. A single Hall-effect unit detects the inner magnets as they pass to provide a single signal. The signals are used to initiate the spark.
U.S. Pat. No. 5,093,617 to Shigemi Murata shows various arrangements of a Hall-effect unit as used in an ignition timing system for internal combustion engines. In the first embodiment, a toothed wheel passes by a front surface of a Hall-effect sensor unit, and the magnet is mounted behind the back surface of the Hall-effect unit. Rotation of the toothed wheel is synchronous with the engine. In all the other embodiments, the toothed wheel passes between the magnet and the Hall-effect unit. The signal generated is used to control engine functions.
U.S. Pat. No. 5,028,868 to Murata et al. shows a flux shutter which is similar to the vane of the aforementioned '926 patent and which passes between the magnet and the Hall-effect unit to generate an engine signal for ignition timing control. In all embodiments, the axial portion of the vane passes between the magnet and the Hall-effect unit. Several different mounting arrangements for the Hall-effect unit and magnet are shown.
U.S. Pat. No. 4,901,704 to Edward J. Safranek reference shows an engine ignition timing structure in which a plurality of magnets are positioned on the outer rim of the flywheel of an engine and rotate therewith. A stator assembly has the coils and four Hall-effect units mounted thereon to sense the passage of the axial portions 6 and 7 of the flux concentrators 29a and 29b which rotate with the flywheel along with a ring magnet 28 which is spaced from the fixed Hall-effect units. The signal generated by the Hall-effect units is used for ignition timing through a circuitry designed to eliminate the dependency of ignition timing on engine RPM.
U.S. Pat. Nos. 4,508,092 and 4,406,272 to Kiess et al. show a distributorless ignition system in which, in one embodiment, a single Hall-effect unit is positioned between two magnets in a spaced apart relationship radially outward from a rotating shaft. A disc is connected to the crank shaft of the engine for rotation with the shaft, and axially extending flange like members at different radial positions pass through the gaps formed between the magnets and the Hall-effect units. This sequentially generates two signals from the Hall-effect unit, one positive and one negative. These signals are processed through differential amplifiers and Schmidt triggers to a micro processor which utilizes the positive signal for operation of the spark in cylinders 1 and 4 and the negative signal for operation of the spark in cylinders 2 an 3. In a second embodiment, there are provided two Hall-effect units with a spaced magnet between them. The same type of flanges move between the magnet and the Hall-effect units to provide the two output signals. A third embodiment is similar to the first and is linearly arranged for detecting linear motion.
All of the devices and apparatuses of the prior art, in the implementation of an electronic ignition system, have one or more shortcomings. Specifically, prior art devices generally require the provision of an external magnetic force. Prior art devices also create, with such magnets, a magnetic field between the magnet and a Hall-effect device and disturb the magnetic flux between the magnet and the Hall-effect device by a rotating disc-like member which must be specially made and adapted to the internal combustion engine adding cost and requiring time consumption for redesign. That is, the devices of the prior art using Hall-effect sensors do not make use of the lobed camshaft already existing in the distributor of an internal combustion engine.
Furthermore, it is recognized by those skilled in the art that precise timing of an engine is critical to its performance. Using the electronic ignition systems of the prior art, while timing may be precisely set at any point in time, it can vary substantially from the preset condition upon the degradation of components, tolerance of parts, variation of battery power due to discharging and charging cycles, variation of the trigger point in the circuitry receiving the output from the sensor, imprecise threshold detection of analog waveforms having inherently wide range detection windows, and other similar factors.
There is a need in the art for an improved electronic ignition system which may operate directly from, and trigger the spark plug timing from, a standard distributor camshaft having a number of lobes and valleys thereon. There is also a need for an improved electronic ignition system which has more accurate and stable timing and dwell characteristics, substantially independent of aging of parts, power variations, and critical threshold requirements, and which can be readily modified or adjusted to produce timing and dwell parameters applicable to a variety of different engines and/or engine types.